1. Field of the Invention
The present invention generally concerns a golf club head. More particularly, the present invention relates to an optimally positioning the center of gravity of a hollow construction golf club head made of a metallic material such as titanium, titanium alloy, stainless steel or similar.
2. Description of the Prior Art
It can be said that the performance of a golf club head, namely, the ball distance traveled and traveling direction, greatly depends upon the position of the center of gravity and moment of inertia of the golf club head. Recently, there are many available types of golf club heads made of metallic materials having high specific strength, respectively, and each having an increased volume and reduced weight. In these situations, many proposals have been made to review and improve the shape and structure of the golf club heads in connection with the problems of the center of gravity position and the moment of inertia.
Generally, geometry of golf club head center of gravity includes parameters such as gravity height, depth and distance (a minimum distance of the center of gravity from the extension of the shaft axis), etc. Therefore, a metallic golf club head of the hollow-construction is designed with major consideration to such parameters of center of gravity to optimally position the center of gravity for a player""s skill and usage of the golf club.
Indeed, the conventional golf club heads manufactured based on the above proposals, for example hollow-con figuration large or xe2x80x9cjumboxe2x80x9d heads made of such a metal having a high specific strength as titanium, for example, had implemented an increased inertia of moment about the center of gravity and also increased spins of a golf ball struck with such a golf club head, thereby allowing average skilled golfers to enjoy an easier swinging of the golf club and increased distance of ball flight. For these purposes, the golf club head was designed for the center of gravity to be lower and deeper in the head. The golf club with such a head will perform it designed function when used by an average skilled golf player who can swing the club at a speed that is not so high. However, when a golf ball is struck with such a golf club by golfers having middle and upper grades of skill who can swing the club head at a higher speed and at a high ratio of meeting the sweet area of the head, too much back spin will be imparted to the golf ball more frequently when unnecessary, which is not any advantage for the skilled players.
Also, if the entire sole portion of the head is designed rather more thicker than the rest to have a low gravity, the vertical moment of inertia of the head about an axis passing through the head center of gravity and parallel to the ground will be unbalanced, so that striking a golf ball at an upper portion of the front face will possibly result in a direction of ball flight not intended or a highs weak ball not traveling a long distance. Also even if other than the sole portion is designed to be more lightweight by thinning of the wall, using a lighter material or otherwise, the head has to be balanced by distributing, to the sole portion, most of the corresponding weight thus reduced thus the head cannot be designed to be larger.
Furthermore, it has been proposed to position only the center of gravity nearer to the front face of the golf club head. In this case, however, since no consideration is given to the gravity height, the center of gravity is positioned higher as it is placed nearer to the front face of the head. The golf club head thus designed will have characteristics suitable only for the highly skilled golf players including professional golfers.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a golf club head having a low gravity maintaining balance the moments of inertia in different directions and characteristics suitable for many different golfers ranging in grade of skill from average to upper levels.
According to the present invention, there is also provided a golf club of 250 cc or more in volume and having a hollow construction, including three gravity adjusting pieces: a piece (A) secured directly on an inner surface of a sole portion of the head in a position nearer to a toe portion, a piece (B) secured directly on the sole inner surface in a position nearer to a back side of the head, and a piece (C) secured directly on the sole inner surface in a position nearer to a heel portion, these gravity adjusting pieces being in a weight relationship of A+Bxe2x89xa6C.
According to the present invention, there is provided a golf club head of 250 cc or more in volume and having a hollow construction, in which an arcuate length (l1) from a front edge of a crown portion of the head to a front edge of a sole portion, a circumferential length (l2) from the crown front edge through the back side to the sole front edge and a gravity depth (D) of the head in a cross section of the head in the direction of the head width at least in a sweet area of a front face, are in a relationship of (l2/l1)xc3x97Dxe2x89xa6100 in the cross section.
According to the present invention, a gravity adjusting piece is secured in a predetermined position of the inner surface of the sole portion of the head to adjust the position of head center of gravity. The gravity adjusting piece has a bar-like shape extending on the inner surface of the sole portion in a position nearer to the front face of the head from the toe portion to the heel portion. Disposing the gravity adjusting piece allows the position of the center of gravity nearer to the front face and lower towards the sole portion (namely, shallow and low gravity), thereby permitting to drastically reduce back spins imparted to a golf ball when struck with the golf club head, and increase the initial angle of ball lifting. Thus, the reduced distance of ball flight frequently experienced by ordinary golfers can be prevented. Also, two such barlike gravity adjusting pieces may be disposed separately, one in a position near the toe of the head and the other near the heel, to shift the center of gravity towards the front face of the head and increase the moment of inertia about a vertical axis through the center of gravity. That is, the center of gravity is placed nearer to the front face while being kept low so that appropriate back spins are imparted the golf ball struck with the club head, result in an increased distance of ball flight and the golf ball can be hit with an increased accuracy owing to the increased moment of inertia. Therefore, the golf club head according to the present invention shows appropriate characteristics suitable for various golfers having average, middle and high grades of skill.
Furthermore, there are disposed on the inner surface of the sole potion two gravity adjusting pieces (A) and (C) separately near the head front face while another piece (B) near the back side such that these pieces are in the relationship in weight of A+Bxe2x89xa6C. Thus, the moment of inertia about a horizontal axis extending through the center of gravity form the heel to toe of the head is increased, contributing to an inhibited variation of the loft angle of the head when striking a golf ball with the head. It is expected that the golf ball will fly over a distance corresponding to the loft angle. Also, the moment of inertia about the axis of the club that is decreased, so the golfers of middle and high skill can well control the golf club head.